High voltage isolation communication devices known in the prior art include optical, magnetic and capacitive devices. Prior art optical devices typically achieve high voltage isolation by employing LEDs and corresponding photodiodes to transmit and receive light signals, usually require high power levels, and suffer from operational and design constraints when multiple communication channels are required. Prior art magnetic devices typically achieve high voltage isolation by employing opposing inductively-coupled coils, and usually require high power levels (especially when high data rates are required). Prior art capacitive devices achieve voltage isolation by employing multiple pairs of transmitting and receiving electrodes, where for example a first pair of electrodes is employed to transmit and receive data, and a second pair of electrodes is employed to refresh or maintain the transmitted signals.
The design of galvanic isolators presents several formidable technical challenges, such as how to reduce power consumption when no data or power signals are being transmitted or received thereby.
One way to reduce power consumption on the sense side of a galvanic isolator is to provide an isolated power supply to the sense side from the transmit side via an integrated DC-DC converter. See FIG. 1, where a circuit diagram of a prior art isolator 10 with an integrated DC-DC converter is illustrated. When transmitter 30 needs to send a data or power signal across galvanic isolation medium 40, it will first perform a DC-DC power transfer across a dedicated power channel to power up receiver 20 located on the sense side of galvanic isolator 40. Once sense side power supply 21 is up, transmitter 30 can then perform a transfer to send the data signals to the sense side from the transmit side. The disadvantage of this method is that the efficiency of power transfer is typically not good due to losses that occur in the isolation medium. One way to improve power transfer efficiency is to design the isolation medium in the power channel to be more efficient than that corresponding to the data channel. However, the disadvantage of doing so is that the system becomes more complex, and thus more expensive.
Another way to reduce power consumption in a galvanic isolator on the sense side is to use an external discrete opto-coupler to send a wake-up pulse from the transmit side 30 to the receive side 20. FIG. 2 shows a prior art circuit 10 that employs an external discrete opto-coupler to receive a wake-up pulse. Once receive side 20 has been powered up, data signals can be transmitted to the sense side 20 from the transmit side 30. The disadvantage of this method is that the extra components required to send and receive the wake-up signal increase board area and also lead to increased costs for electronic components.
See also Baoxing Chen, “iCoupler® Products with isoPower™ Technology: Signal and Power Transfer Across Isolation Barrier Using Microtransformers”, published by Analog Devices, where further information concerning galvanic isolators is to be found.
What is needed is a galvanic isolator that consumes reduced power, that may be built at low cost, or that has other advantages that will become apparent after having read and understood the specification and drawings hereof.